In the manufacturing industries, there is a large and continuously growing demand for flat steel (sheet, strip, coil, etc) coated with protective alloys such as zinc and aluminum based alloys. To manufacture these products, a coating process known as hot dip melt coating is used. A simplified description of the process will now be described.
Elongated steel sheet material is hot and/or cold rolled to form a “strip” which may be wound into a “coil”. The coiled steel strip is uncoiled and passed through a bath of molten metal that coats the surface of the strip. FIG. 1 shows a highly simplified diagram of the apparatus hereinafter designated as a hot dip melt coating apparatus 1. The apparatus includes a melt pot 2 filled with molten metal 3 to be coated onto the bare steel strip 4. The bare steel strip 4 enters the hot dip melt coating apparatus 1 through a snout 5. The interior of the snout 5 has a reducing or inert atmosphere to prevent the bare steel strip 4 from oxidizing. The bare steel strip 4 travels downward into the molten metal 3 at the melt surface 6. This region within the snout 5 where the bare steel strip 4 first enters the molten metal 6 is of critical importance to the quality of the final coated product. Once the steel strip is fully submerged in the molten metal 3, it is passed around a roller and up out of the molten metal 3. The emerging strip is coated with metal. Once the coated strip exits the molten metal 3, various means are used to control coating thickness and uniformity 8. Once the molten coating has cooled and/or reacted with the surface of the steel strip, the coated steel strip 4 is once again coiled (not shown) and the coils are sold to manufacturing customers.
Surface quality standards for coated products are becoming increasingly stringent as customers requirements become more demanding. As is probably apparent, the conditions under which the molten metal is deposited onto the steel strip play a large roll in the quality of the coating and the final coated strip product. However, because of the conditions under which hot dip melt coating operations occur, the “melt pot” is basically a black box into which bare steel strip, coating metal and energy are input and coated steel strip is output. It is extremely difficult to control and monitor the conditions within the “black box” and, as such, when there are quality problems, it is often not known where the problems arose. Thus, even when changes to the system are made, the changes to the output product are not known quickly and require quality analysis of the product. If the desired improvements are not achieved or the quality worsens, hot dip coating line (HDCL) operators must make additional educated guesses at what is causing the quality errors. Alleviating the quality issues is very important because strip material which is not of superior quality will, at best, be sold at a very unfavorable price, and at worst, be scrapped at a significant loss.
As described above, the hot dip melt pot is basically a black box. In an attempt to better understand and more readily control the interior workings of the black box, viewing ports have been provided in what is called the “snout” of the coating apparatus. These view ports allow visual access to the interior of the hot dip melt pot snout. Unfortunately, the interior of the black box is relatively dark and it is very difficult to observe any useful information. Thus, illumination ports were added to the snout into which sources of illumination were shone. Now, the interior is illuminated by light. Further, visible light cameras were mounted into the view ports to view the interior of the hot dip melt pot snout. Unfortunately, this setup was also inadequate for detecting adequate information of the interior of the hot dip melt pot snout. The molten metal and metal coated surfaces are highly reflective and the light from the illumination source essentially washes out any details of the interior of the black box. The images that were received from the camera were essentially unintelligible areas of pure white and black. No useful data could be observed. Furthermore, the illumination ports would coat with molten metal dust reducing the illumination over time. Thus the ports would need to be replaced increasing the risk that oxygen and/or water vapor would enter the melt pot interior, which is typically a reducing or inert atmosphere. Similarly, the viewing ports would coat with the dust and need to be cleaned or replaced.
Thus there is a need in the art for a system to usefully image the interior of the hot dip melt pot snout. The system must provide for high visual contrast and preferably high resolution imaging.